The objective of this project is to develop a minimally invasive and multimodal neurosurgical monitoring system that is capable of simultaneously measuring cerebral blood flow (CBF) and intracranial pressure (ICP) continuously and in real time. This innovative approach will combine the measurement modalities with the ability to drain cerebrospinal fluid (CSF) to control ICP with the same device. Each year in the U.S. there are 370,000 incidents of traumatic brain injury (TBI) and 100,000 subsequent deaths. Injury results from a primary trauma and a later secondary injury caused by local ishemia (deficient blood supply) in viable tissue. Monitoring and interventional therapies to prevent secondary injury attempt to maintain an adequate level of CBF to viable tissue by controlling ICP below a threshold level. While in practice CBF is not typically monitored, ICP is used to indirectly assess ischemic risk. Direct, real-time and continuous monitoring of CBF will help guide therapy, provide an early warning for ischemia, vasospasm, and neurophysiologic deterioration, allow customization of patient-specific therapy and help understand neurophysiology. For the neurosurgeon, the measurement of CBF at the bedside has been long desired and sought after. In Phase II, the multimodal minimally invasive and instrumented ventricular catheter will be designed and developed. Also, the multimodal monitor and associated software will be developed and utilized in a series of studies with head-injured patients. Custom intracranial access hardware will be developed to facilitate the introduction the catheter into cerebral tissue. The monitor will have a color LCD display and an intuitive user interface. CBF and ICP will be displayed in numerical and graphical form continuously and in real time. A series of clinical studies will be performed to monitor CBF in patients with traumatic injury or aneurismal subarachnoid hemorrhage. The aim of this study is to confirm the high level of clinical value CBF and ICP monitoring has as an early warning of clinically relevant events.